Driving circuit for light emitting element, exposure head, and image forming apparatus

ABSTRACT

Each data line includes base parts covering contact holes and line parts extending in an array direction of pixel circuits and connecting adjacent base parts to each other. The line parts have a smaller width in a direction perpendicular to the array direction than the base parts and are connected to the base parts while being offset in the direction perpendicular to the array direction from each other on both sides of at least two base parts that include first and second base parts. A connection position of the first base part with the line part on one side among both sides of the base units is located on the pixel circuit side with respect to the other side, and a connection position of the second base part on the one side is located on an opposite side to the pixel circuit side with respect to the other side.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a driving circuit for a light emittingelement, an exposure head, and an image forming apparatus.

2. Description of the Related Art

An exposure head that uses light emitting elements such as organicelectroluminescence (EL) elements and is mounted to a printer or thelike, for example, is constituted by linearly arranging a plurality ofpixels having the light emitting elements on a substrate. For thatreason, the exposure head has a shape to be elongated in an arraydirection of the pixels to have a high aspect ratio. At this time, theexposure head preferably has a smaller area as more patterns can beproduced at the time of mass production so that costs are reduced. Inparticular, a variation in the length in a traversal directionsignificantly affects the area, and this length is preferably set to beshorter as much as possible. At the same time, high speed driving suchas an increase in a printing speed is also demanded for the exposurehead. To realize these configurations, block driving for collectivelywriting data to a plurality of pixels by a plurality of data lines ispreferably employed.

A plurality of leading lines are connected to a single data line via acontact hole in the block driving. Since a part covering the contacthole by the data lines tends to be wider than the other part, a problemoccurs that it is difficult to decrease a distance between the datalines, and it is difficult to reduce the area occupied by the datalines.

Japanese Patent Laid-Open No. 2011-002502 discloses a technology ofnarrowing line intervals by shifting land parts covering the contactholes in a line lengthwise direction.

However, according to Japanese Patent Laid-Open No. 2011-002502, a firstland part is formed so as to protrude from a first line part in only onedirection, and a second land part is formed so as to protrude from asecond line part in only the same direction as the protrusion of thefirst land part. For that reason, the interval of the adjacent lines isnot sufficiently narrowed. In addition, Japanese Patent Laid-Open No.2011-002502 does not disclose a manner in which the line interval isnarrowed in a case where a plurality of lines each having three or moreland parts are arranged.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-describedproblems in the related art and provides a driving circuit for a lightemitting element in which the area occupied by a plurality of data linesis reduced.

To solve the above-described problems, the present invention provides adriving circuit for a light emitting element, the driving circuitincluding:

a plurality of pixel circuits aligned in line;

a plurality of data lines which are arranged to extend in parallel to anarray direction of the pixel circuits and not to overlap with a regionof the aligned pixel circuits and which supply data signals to the pixelcircuits; and

a plurality of leading lines that are arranged on a layer different fromthe data lines and connected to the data lines via contact holes and tothe pixel circuits, in which

each of the plurality of data lines includes a plurality of base partsthat cover the contact holes and a plurality of line parts that extendin the array direction of the pixel circuits and connect adjacent baseparts to each other, and the line parts have a smaller width in thedirection perpendicular to the array direction of the pixel circuitsthan the base parts and are connected to the base parts while beingoffset in the direction perpendicular to the array direction of thepixel circuits from each other on both sides of at least two base parts,and

the at least two base parts include a first base part and a second basepart, a connection position of the first base part with the line part onone side among both sides of the base units being located on the pixelcircuit side with respect to the other side, and a connection positionof the second base part with the line part on the one side among theboth sides of the base units being located on an opposite side to thepixel circuit side with respect to the other side.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example configuration of an exposurehead that uses a driving circuit for a light emitting element accordingto an exemplary embodiment of the present invention.

FIG. 2 illustrates details of a partial data line part of FIG. 1.

FIG. 3 is a timing chart for data transmitted to the data line of FIG.2.

FIG. 4 illustrates another example of the detail of the partial dataline part.

FIG. 5 illustrates an example circuit for a pixel.

FIG. 6 is a schematic diagram of an image forming apparatus includingthe exposure head that uses the driving circuit for the light emittingelements according to the exemplary embodiment of the present invention.

FIG. 7 illustrates details of a partial data line part.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, the present invention will be described in detail by usingthe drawings. Driving circuit for light emitting element and exposurehead

An example in which a driving circuit for a light emitting elementaccording to an exemplary embodiment of the present invention is used asan exposure head that irradiates a photosensitive drum with light toexpose a latent image will be described by using FIG. 1 and FIG. 2. FIG.1 is a schematic diagram of an example configuration of an exposure headthat uses a driving circuit for a light emitting element according to anembodiment of the present invention. FIG. 2 illustrates details of apartial data line part of FIG. 1.

As illustrated in FIG. 1, the exposure head according to the embodimentof the present invention is constituted by forming a plurality of pixelcircuits 2 to be arranged in one direction on a substrate 1. Forexample, a glass substrate, a silicon substrate, or the like can be usedas the substrate 1. A light emitting element 11 is connected to each ofthe pixel circuits 2, and the pixel circuit 2 and the light emittingelement 11 constitute a pixel. The light emitting elements 11 arearranged so as to be aligned in line in an array direction of the pixelcircuits 2, but the light emitting elements 11 may be arranged, forexample, in a zigzag alignment or the like without being aligned inline, and dummy light emitting elements may be arranged in plural lines.For example, a light emitting diode (LED), an inorganic EL element, anorganic EL element, or the like may be used as the light emittingelement 11.

With regard to the pixel circuits 2, a length in a directionperpendicular to the array direction of the pixel circuits 2 is longerthan a length in the array direction of the pixel circuits 2. The pixelcircuits 2 illustrated in FIG. 1 substantially have a rectangular shape.The pixel circuits 2 are divided into a plurality of blocks constitutedby a plurality of adjacent pixel circuits. Specifically, n pieces (n isan integer higher than or equal to 2 and is preferably 3 or higher) ofthe adjacent pixel circuits 2 are grouped as one block. Then, m blocks(m is an integer higher than or equal to 2 and is preferably 3 orhigher) are arranged in total. Furthermore, the respective blocks arealigned in line in the same direction as the array direction of thepixel circuits 2.

A data line 3 is a line on which a data signal is transmitted. The dataline 3 is arranged in a region on an extension line in the directionperpendicular to the array direction of the pixel circuits 2. Accordingto the present exemplary embodiment, n data lines 3 corresponding to thenumber of the pixel circuits 2 constituting one block are aligned. Thedata line 3 and the pixel circuit 2 are connected to each other via aleading line 32. According to the present exemplary embodiment, mleading lines 32 corresponding to the number of blocks are connected toone data line 3, and the data signal is supplied to the pixel circuits 2in the respective blocks. According to the present exemplary embodiment,the leading lines 32 extend in the direction perpendicular to the arraydirection of the pixel circuits 2. It is noted that in FIG. 1, the dataline 3 is represented by a straight line extending in the arraydirection of the pixel circuits 2 but has a shape illustrated in FIG. 2in actuality. Details of the data line 3 will be described below.

Controls signals such as a clock signal CK, CKB, a data signal ST, and Pare input to a scanning circuit 4. The scanning circuit 4 outputs ascanning signal to a scanning line 8 for each block to supply the pixelcircuits with the scanning signal. The scanning circuit 4 includes shiftregisters, and the scanning signals are output in units of blocks whiletiming points are shifted. The shift registers in the scanning circuit 4are arranged such that the signals travel in the array direction of thepixel circuits 2. It is noted that FIG. 1 illustrates the configurationin which the scanning signal is input to the pixel circuit 2 by onescanning line 8, but the number of the scanning lines 8 is not limitedto this.

A power supply voltage is supplied to all the pixel circuits 2 and thelight emitting elements 11 via a first power supply line 5 and a secondpower supply line. A plurality of second power supply lines are arrangedin a region 6A, and the region 6A is arranged so as to be overlappedwith the light emitting elements 11 and the pixel circuits 2. The secondpower supply lines are formed on a layer different from the data lines3, the leading lines 32, and the lines of the pixel circuits 2 in theregion 6A. The above-described signals and power supply voltage aresupplied onto the substrate 1 by respective terminal parts 7. It isnoted that the second power supply lines are transferred to the otherlayer in the vicinity of the terminal parts 7 to be connected to theterminal parts 7.

FIG. 2 illustrates details of a part equivalent to four blocks of thedata line parts in FIG. 1. As described above, the pixel circuits 2 aredivided into the m blocks each constituted by the n adjacent pixelcircuits. In FIG. 2, the pixel circuit belonging to Block 1 aresequentially denoted as 1-1, 1-2, . . . , 1-n from the left side towardsthe paper plane. The same applies to Block 2 and subsequent blocks, andFIG. 2 illustrates blocks up to Block 4. As illustrated in FIG. 2, thedriving circuit according to the exemplary embodiment of the presentinvention includes n data lines 3 (D1 to Dn) corresponding to the numberof the pixel circuits 2 constituting one block. The leading lines 32that connect the data lines 3 to the pixel circuits 2 are arranged on alayer different from the data lines 3 via an insulating layer and areconnected to the data lines 3 via contact holes 34 formed on theinsulating layer. Each of the plurality of data lines 3 includes aplurality of base parts 33 covering the contact holes 34 and a pluralityof line parts 35 extending in the array direction of the pixel circuits2 and connecting the adjacent base parts 33 to each other. According tothe present exemplary embodiment, each of the data lines 3 includes mbase parts 33 corresponding to the number of blocks and is connected tothe m leading lines 32. Specifically, as illustrated in FIG. 2, a dataline D1 is connected to a leading line connected to a pixel circuit 1-1in the Block 1, a leading line connected to a pixel circuit 2-n in theBlock 2, . . . , and a leading line connected to the pixel circuit (m-1in a case where m is an odd number or m-n in a case where m is an evennumber) in the Block m. The same applied to a data line D2 andsubsequent data lines. That is, one leading line to one block extendsfrom one data line 3.

The line parts 35 are constituted by a low-resistance line layer such asaluminum lines and have a smaller width in the direction perpendicularto the array direction of the pixel circuits 2 than the base parts 33.The line parts 35 are offset on both sides of at least two base parts 33(all the base parts 33 according to the present exemplary embodiment)from each other in the direction perpendicular to the array direction ofthe pixel circuits 2 to be connected to the base parts 33. For thatreason, the mutual base parts 33 of the adjacent data lines 3 arearranged while being shifted in the array direction of the pixelcircuits 2 from each other, so that a distance between the adjacent datalines can be shortened as compared with a case where the line parts 35are connected without being offset on the both sides of the base parts33 from each other (central axes are matched to each other). From theabove-described viewpoint, as illustrated in FIG. 2, the line parts 35are connected to be flush with the base parts 33 on the both sides ofthe base parts 33.

The base part 33 includes a first base part 33 a and a second base part33 b. A connection position of the first base part 33 a with the linepart 35 on one side of the base part 33 (left side towards the paperplane in FIG. 2) is located on a pixel circuit 2 side with respect tothe other side (right side towards the paper plane in FIG. 2). Aconnection position of the second base part 33 b on the one side (leftside towards the paper plane in FIG. 2) is located on an opposite sideto the pixel circuit 2 side with respect to the other side (right sidetowards the paper plane in FIG. 2).

To shorten the distance between the adjacent data lines 3, the mutualbase parts nearest to the adjacent data lines 3 are preferably both thefirst base parts 33 a or both the second base parts 33 b. In FIG. 2, thebase parts 33 to which the leading lines 32 connected to the pixelcircuits 2 belonging to the same block are connected are unified to beeither the first base parts 33 a or the second base parts 33 b.

At this time, it is assumed that the base parts are only the first baseparts 33 a as illustrated in FIG. 7. The mutual line parts 35 areshifted in the direction perpendicular to the array direction of thepixel circuits 2 from each other by a difference (ΔL) of line widths ofthe base part 33 and the line part 35 on both sides of one base part.Since the data line 3 includes the m base parts, the mutual line parts35 on both ends are shifted in the direction perpendicular to the arraydirection of the pixel circuits 2 from each other by ΔL×m. Therefore,even if the distance between the adjacent data lines 3 is short, anextra region occupied by the data lines corresponding to ΔL×m needs tobe secured. The light emitting elements 11 and the pixel circuits 2arranged to be adjacent to the data lines 3 are preferably aligned inline so as to be parallel to the long side of the substrate 1. In theseparts, it is also difficult to effectively use the shifted spacecorresponding to ΔL×m. The same also applies to a case where the baseparts are only the second base parts 33 b.

In contrast to this, the base part 33 includes the first base part 33 aand the second base part 33 b in the driving circuit according to theexemplary embodiment of the present invention. For that reason, thefirst base part 33 a and the second base part 33 b mutuallycounterbalance a shift amount of the line parts 35, and the regionoccupied by the data lines can be reduced. In FIG. 2, each of the datalines 3 alternately includes the first base part 33 a and the secondbase part 33 b. For that reason, the shift amount of the mutual lineparts 35 on both ends is 0 in a case where the block number m is an evennumber or ΔL in a case where the block number m is an odd number. Tominimize the shift amount of the mutual line parts 35 on the both ends,each of the data lines 3 preferably has the same numbers of the firstbase part 33 a and the second base part 33 b. It is however noted that,when at least one of the first base part 33 a and at least one of thesecond base part 33 b are prepared, even if the numbers of the firstbase part 33 a and the second base part 33 b are different from eachother, the effect of counterbalancing the shift amount can be obtained,and it is possible to reduce the region occupied by the data lines.

The arrangement of the first base parts 33 a and the second base parts33 b is not limited to the arrangement illustrated in FIG. 2, and forexample, as illustrated in FIG. 4, the first base parts 33 a or thesecond base parts 33 b may be continuously arranged.

Next, a method of performing data writing from the data line of thedriving circuit according to the exemplary embodiment of the presentinvention will be described while the case of FIG. 2 is used as anexample. FIG. 3 is a timing chart for data transmitted to the data lineof FIG. 2.

To write data in each block in sequence like the Block 1, the Block 2, .. . , the Block m, the data is transmitted to the relevant pixelcircuits 2 connected to the respective data lines 3. In general, thedata is transmitted from the data line D1 in any block in the pixelcircuits 2 (1-1, 2-1, . . . , m-1) on the left end towards the paperplane in the block. However, according to the mode of FIG. 2, the dataline D1 is connected to the pixel circuit 1-1 in the Block 1 but isconnected to the pixel circuit 2-n in the Block 2. Similarly, the dataline Dn is connected to the pixel circuit 1-n in the Block 1 but isconnected to the pixel circuit 2-1 in the Block 2. Therefore, the k-thdata is written to the k-th data line (k is a natural number higher thanor equal to 1 and lower than or equal to n) in the block to which thepixel circuits 2 connected to the base parts 33 unified to be one groupamong a group of the first base parts 33 a or a group of the second baseparts 33 b belong. The [n−(k−1)]-th data is written to the k-th dataline in the block to which the pixel circuits 2 connected to the baseparts 33 unified to be the other group belong. Specifically, the data istransmitted to the data line 3 from the first in ascending sequence inthe odd-numbered block, and the data is transmitted to the data line 3from the n-th in descending sequence in the even-numbered block.

FIG. 5 illustrates an example circuit for a pixel constituted by thepixel circuit 2 and the light emitting element 11. A circuitconfiguration will be described. The pixel circuit 2 is constituted bytwo PMOS transistors and one holding capacitance C1. A scanning signalP1 is input to a gate electrode of a switching transistor Tr1corresponding to a selection transistor, and the leading line 32 isconnected to one of a source and a drain. The other end of the source orthe drain is connected to a gate of a driving transistor Tr2. A sourceof the driving transistor Tr2 is connected to the first power supplyline 5, and a drain thereof is connected to an anode electrode of thelight emitting element 11. The holding capacitance C1 is arrangedbetween the gate and the source of the driving transistor Tr2 and holdsthe data voltage written in the pixel circuit 2. Furthermore, a cathodeof the light emitting elements 11 is connected to a second power supplyline 6 corresponding to a common potential commonly provided to all thepixels. One of the anode electrode and the cathode electrode is set as alight retrieval surface and is therefore constituted by a transparentelectrode (for example, indium tin oxide (ITO), indium zinc oxide (IZO),or the like).

Circuit operation will be described. The switching transistor Tr1 isturned ON at the timing point when the data corresponding to therelevant pixel is set onto the data line 3. Subsequently, the data iswritten in the holding capacitance C1. After that, the switchingtransistor Tr1 is turned OFF, so that the data is held in the pixelcircuits 2. At the same time, a driving current in accordance with agate-source voltage of the driving transistor Tr2 flows from the drivingtransistor Tr2 to the light emitting element 11. According to thepresent exemplary embodiment, the example in which the pixel circuit 2is constituted by the PMOS has been illustrated, but the configurationis not limited to this transistor (Tr) polarity. Specifically, a circuitconstituted by a single channel of an NMOS or a circuit where the NMOSand the PMOS both exist may also be used.

According to the above-described exemplary embodiment, a type of thelight emitting element is not limited, but the present invention ispreferably used for a driving circuit that controls lighting of theorganic EL element, in particular, a driving circuit where the blockdriving is performed. In addition, the example in which the lightemitting elements are used for the exposure head has been described, butthe present invention can also be applied to a driving circuit for alinear light source in which the light emitting elements are arranged inline or an active matrix type display, or the like.

Image Forming Apparatus

An image forming apparatus provided with the exposure head that uses thedriving circuit for the light emitting elements according to theembodiment of the present invention will be described by using FIG. 6.An image forming apparatus 100 includes a recording unit 104. Therecording unit 104 is provided with a photosensitive drum 105, a charger106, an exposure head 107 provided with the driving circuit for thelight emitting elements according to the embodiment of the presentinvention, a developer 108, and a transfer device 109. The image formingapparatus 100 further includes a conveyance roller 103 and a fuser 110.

First, in the recording unit 104, a front face of the cylindricalphotosensitive drum 105 is uniformly charged by the charger 106, and theexposure head 107 emits light in accordance with data to form anelectrostatic latent image on the photosensitive drum 105. Theelectrostatic latent image can be controlled by the exposure amount(illuminance, time) of the exposure head 107. Next, in the recordingunit 104, toner is adhered to the electrostatic latent image by thedeveloper 108, and the toner adhered to the electrostatic latent imageis transferred to a sheet 102 by the transfer device 109. In thismanner, the toner on the sheet 102 on which the image data istransferred via the recording unit 104 is fused by the fuser 110, andthe sheet 102 is discharged. It is noted that the timing point at whichthe sheet 102 is conveyed to the recording unit 104 by the conveyanceroller 103 can be arbitrarily set. According to the present exemplaryembodiment, the description has been given while taking the example inwhich the recording unit 104 is the single monochrome image formingapparatus, but the configuration is not limited to this. A color imageforming apparatus provided with a plurality of recording units 104 mayalso be used.

According to the present exemplary embodiment of the present invention,the area occupied by the data lines is small, so that the substrate sizecan be reduced, and the frame can be narrowed.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2013-224922, filed Oct. 30, 2013, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A driving circuit for a light emitting element,the driving circuit comprising: a plurality of pixel circuits aligned inline; a plurality of data lines which are arranged to extend in parallelto an array direction of the pixel circuits and not to overlap with aregion of the aligned pixel circuits and which supply data signals tothe pixel circuits; and a plurality of leading lines that are arrangedon a layer different from the data lines and connected to the data linesvia contact holes and to the pixel circuits, wherein each of theplurality of data lines includes a plurality of base parts that coverthe contact holes and a plurality of line parts that extend in the arraydirection of the pixel circuits and connect adjacent base parts to eachother, and the line parts have a smaller width in the directionperpendicular to the array direction of the pixel circuits than the baseparts and are connected to the base parts while being offset in thedirection perpendicular to the array direction of the pixel circuitsfrom each other on both sides of at least two base parts, and whereinthe at least two base parts include a first base part and a second basepart, a connection position of the first base part with the line part onone side among both sides of the base units being located on the pixelcircuit side with respect to the other side, and a connection positionof the second base part with the line part on the one side among theboth sides of the base units being located on an opposite side to thepixel circuit side with respect to the other side.
 2. The drivingcircuit for the light emitting element according to claim 1, wherein themutual base parts for the adjacent data lines are arranged while beingshifted in the array direction of the pixel circuits from each other. 3.The driving circuit for the light emitting element according to claim 1,wherein the line parts are connected to be flush with the base parts onboth sides of opposite periphery of the base parts.
 4. The drivingcircuit for the light emitting element according to claim 1, whereineach of the plurality of data lines alternately includes the first basepart and the second base part.
 5. The driving circuit for the lightemitting element according to claim 1, wherein each of the plurality ofdata lines includes the same numbers of the first base parts and thesecond base parts.
 6. The driving circuit for the light emitting elementaccording to claim 1, wherein the leading lines extend in the directionperpendicular to the array direction of the pixel circuits.
 7. Thedriving circuit for the light emitting element according to claim 1,wherein the plurality of pixel circuits are divided into a plurality ofblocks each constituted by a plurality of adjacent pixel circuits, andthe base parts to which the leading lines connected to the pixelcircuits belonging to the same block are connected are unified to be thefirst base parts or the second base parts.
 8. The driving circuit forthe light emitting element according to claim 7, wherein the number ofpixel circuits belonging to the block is n, the k-th data is written tothe k-th data line where k is a natural number higher than or equal to 1and lower than or equal to n in a block to which the pixel circuitsconnected to the base parts unified to be one group among a group of thefirst base parts and a group of the second base parts belong, and the[n−(k−1)]-th data is written to the k-th data line in a block to whichthe pixel circuits connected to the base parts unified to be the othergroup among the group of the first base parts and the group of thesecond base parts belong.
 9. The driving circuit for the light emittingelement according to claim 1, wherein the pixel circuit includes adriving transistor configured to supply a driving current to the lightemitting element connected to the pixel circuit, and a selectiontransistor configured to supply a data signal supplied via the dataline, to the driving transistor.
 10. The driving circuit for the lightemitting element according to claim 9, further comprising: a scanningcircuit, wherein a scanning line connected to the scanning circuit isconnected to a gate electrode of the selection transistor, and a controlsignal is transmitted through the scanning line.
 11. An exposure headcomprising the driving circuit for the light emitting element accordingto claim
 1. 12. An image forming apparatus comprising the exposure headaccording to claim 11.